No flow underfill

ABSTRACT

A method for making a microelectronic assembly includes providing a microelectronic element with first conductive elements and a dielectric element with second conductive elements. At least some of either the first conductive elements or the second conductive elements may be conductive posts and other of the first or second conductive elements may include a bond metal disposed between some of the conductive posts. An underfill layer may overly some of the first or second conductive elements. At least one of the first conductive elements may be moved towards the other of the second conductive elements so that the posts pierce the underfill layer and at least deform the bond metal. The microelectronic element and the dielectric element can be heated to join them together. The height of the posts above the surface may be at least forty percent of a distance between surfaces of the microelectronic element and dielectric element.

BACKGROUND OF THE INVENTION

In the construction of semiconductor chip package assemblies, it hasbeen found desirable to interpose encapsulant material or an underfillbetween and/or around elements of semiconductor packages in an effort toreduce and/or redistribute the strain and stress on the connectionsbetween the semiconductor chip and a supporting circuitized substrate ordielectric element during operation of the chip, and to seal theelements against corrosion, as well as to insure intimate contactbetween the encapsulant, the semiconductor die and the other elements ofthe chip package.

Various methods have been devised to encapsulate semiconductor chippackage assemblies and the like. Nevertheless, despite all of the effortwhich has been devoted to development of microelectronic encapsulationtechniques, there are unmet needs for further improvements.

SUMMARY OF THE INVENTION

A method for making a microelectronic assembly can include providing afirst component having a first surface and first conductive elementsprojecting above the first surface, and a second component having asecond surface and second conductive elements projecting above thesecond surface. At least one of the first or second components may be amicroelectronic element, at least some of the first conductive elementsor at least some of the second conductive elements may be beingsubstantially rigid conductive posts, and the posts may have a heightabove the respective surface from which the posts project of at leastforty percent of a distance between the first and second surfaces. Abond metal may be disposed on at least either the at least some firstconductive elements or the second conductive elements, and an underfilllayer may overlie at least some of the first conductive elements or atleast some of the second conductive elements. The method may includemoving at least one of the first conductive elements towards another ofthe second conductive elements such that the substantially rigid postspierce the underfill layer and at least deform the bond metal. Themethod may include heating the first and second components to a joiningtemperature until the bond metal flows along edges of the posts andelectrically joins the first and second components. The bond metal maycontact the edges along at least one half the height of the posts.

In another aspect of the present invention, a method for making amicroelectronic assembly can include providing a microelectronic elementhaving a first surface and first conductive elements projecting abovethe first surface, and a dielectric element having a second surface andsecond conductive elements projecting above the second surface. At leastsome of the first conductive elements or at least some of the secondconductive elements may be a substantially rigid conductive posts, andthe other of the first or second conductive elements may include a bondmetal juxtaposed with the at least some conductive posts. The posts mayhave a height above the respective surface from which the posts project,and an underfill layer overlying at least some of the first conductiveelements or at least some of the second conductive elements. The methodmay include moving at least one of the first conductive elements towardsthe other of the second conductive elements such that the substantiallyrigid posts pierce the underfill layer and at least deform the bondmetal. The method may include heating the microelectronic element andthe dielectric element to a joining temperature until the bond metalflows along edges of the posts to contact the edges along at least onehalf the height of the posts and electrically joins the microelectronicelement with the dielectric element. The height of the posts above thesurface from which they project may be at least forty percent of adistance between the first and second surfaces.

In one embodiment, the first conductive elements include the bond metaland the at least some conductive posts are second conductive elements ofthe dielectric element.

In one embodiment, the at least some posts are first conductive elementsof the microelectronic element and the second conductive elementsinclude the bond metal.

In one embodiment, the step of moving at least one of the firstconductive posts towards the other of the second conductive elementsincludes the substantially rigid posts piercing the bond metal.

In one embodiment, the step of moving at least one of the firstconductive elements toward the other includes penetrating the bond metalto a depth of at least 25% of a height of the solder above therespective one of the first or second surfaces.

In one embodiment, prior to the step of deforming the bond metal, traceamounts of the underfill layer are pushed into the bond metal by theconductive posts.

In one embodiment, the first component may be a chip or aninterconnection element.

In one embodiment, the first and second components may be chips or thesecond component may be an interconnection element.

In one embodiment, at least some of the first conductive elements may besubstantially rigid posts; or at least some of the first conductiveelements may be conductive pads; or at least some of the secondconductive elements may be substantially rigid posts; or at least someof the second conductive elements may be contact pads.

In one embodiment, the underfill may overlie the first conductiveelements; or the underfill may overlie the second conductive elements;or the underfill may overlie the first and second conductive elements.

In one embodiment, the first component may be a microelectronic element,at least some of the first conductive elements may be contact pads, andat least some of the second conductive elements are substantially rigidposts. Alternatively, the second component may be an interconnectionelement or a microelectronic element. In another alternate embodiment,the step of providing may include providing a bond metal on the at leastsome of the substantially rigid posts or providing a bond metal on theat least some of the contact pads.

In one embodiment, the first component may be a microelectronic element,at least some of the first conductive elements may be substantiallyrigid posts, and at least some of the second conductive elements may becontact pads. Alternatively, the second component may be aninterconnection element or a microelectronic element.

In one embodiment, the first component may be a microelectronic element,at least some of the first conductive elements may be substantiallyrigid posts, and at least some of the second conductive elements may besubstantially rigid posts. Alternatively, the second component may be aninterconnection element or a microelectronic element.

In accordance with another aspect of invention, a microelectronicassembly may include a first component, a second component, a bondmetal, and an underfill layer. The first component may have a firstsurface and first conductive elements projecting above the firstsurface. The second component may have a second surface and secondconductive elements projecting above the second surface. The at leastone of the first or second components may be a microelectronic element,at least some of the first conductive elements or at least some of thesecond conductive elements may be substantially rigid conductive postsand may have a height above the respective surface from which the postsproject. The bond metal may be disposed between respective pairs ofconductive elements, the respective pairs each including at least one ofthe posts and at least one of the first or second conductive elementsconfronting the at least one post. The bond metal may also contact edgesof the posts along at least one half the height of the posts. Theunderfill layer may contact and bond the first and second surfaces ofthe first and second components. A residue of the underfill layer may bepresent at least one of interfacial surfaces between at least some ofthe posts and the bond metal, or the residue of the underfill layer maybe present within the bond metal.

In one embodiment, the first component may be a microelectronic elementand the second component may be a dielectric element. Alternatively, themicroelectronic element may be a chip.

In one embodiment, the first component may be a dielectric element.

In one embodiment, the first component and the second component may bemicroelectronic elements; or the first conductive elements may be theconductive posts.

In one embodiment, the second conductive elements may be the conductiveposts.

In one embodiment, both the first conductive elements and the secondconductive elements may be the conductive posts.

In one embodiment, a bonding metal may be deposited on at least one ofthe conductive posts.

In one embodiment, a solder mask may be provided adjacent the conductiveposts; or at least a portion of the conductive posts may be coated witha material resistant to a bonding metal.

In one embodiment, the bond metal may cover one half or less of a heightof at least one of the conductive posts.

In one embodiment, the second conductive elements may be the conductiveposts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an embodiment in accordance with one embodiment of the presentinvention.

FIG. 2 is a top view of FIG. 1( c).

FIG. 2A is an exploded view of a portion of FIG. 1( f).

FIG. 3 is an alternate embodiment of FIG. 1.

FIG. 4 is an alternate embodiment of FIG. 1.

FIG. 5 is another alternate embodiment of FIG. 1.

FIG. 6 is another alternate embodiment of FIG. 1.

FIG. 7 is an alternate embodiment of FIG. 6.

FIG. 8 is another alternate embodiment of FIG. 1.

FIG. 9 is an alternate embodiment of a portion of FIG. 1F.

FIG. 10 is a system in accordance with an embodiment of the invention.

FIG. 11 is a schematic depiction of a system according to one embodimentof the invention.

DETAILED DESCRIPTION

FIG. 1 is a sectional view of a method of preparing a microelectronicpackage 100 (FIG. 1( f)) in accordance with an embodiment of the presentinvention. As shown, the microelectronic package 100 includes amicroelectronic element 30 and a dielectric element 50 with conductiveposts 40 exposed thereat. (FIGS. 1( a)-(b).)

Referring to FIG. 1( a), in one example, the microelectronic element 30can be a single “bare”, i.e., unpackaged die, e.g., a semiconductor chiphaving microelectronic circuitry thereon. A plurality of contacts, e.g.,bond pads 20 can be exposed at a contact-bearing surface 32 of asemiconductor die and may be arranged in one or more rows exposed atsuch surface.

As used in this disclosure, a statement that an electrically conductiveelement is “exposed at” a surface of a dielectric element indicates thatthe electrically conductive element is available for contact with atheoretical point moving in a direction perpendicular to the surface ofthe dielectric element toward the surface of the dielectric element fromoutside the dielectric element. Thus, a terminal or other conductiveelement which is exposed at a surface of a dielectric element mayproject from such surface; may be flush with such surface; or may berecessed relative to such surface and exposed through a hole ordepression in the dielectric element.

A bond metal 10, such as solder, indium, tin, or a combination thereof,for example, may be joined to bond pads 20 of the microelectronicelement 30.

Referring to FIG. 1( b), in one embodiment, a dielectric element 50,such as for example, a substrate, chip carrier, tape, etc. may beprovided that has conductive elements exposed at a surface thereof. Inone embodiment, the dielectric element 50 has a length L1 that isgreater than the length L2 of the microelectronic element.Alternatively, the lengths of the dielectric and microelectronicelements can be the same. In the embodiment shown, the conductiveelements are substantially rigid metal posts 40 extending above oroutwardly from the top surface of the dielectric element 50. The posts40 may be prepared using any methods known in the art.

For example, as described in U.S. Pat. No. 6,177,636 to Fjelstad, thedisclosure of which is incorporated herein by reference, a plurality ofsubstantially rigid, elongated posts protruding parallel to one anotherfrom a surface of a substrate can be formed by attaching a conductivesheet to a substrate surface and then selectively removing portions ofthe conductive sheet. The metal sheet can consist essentially of copperor may have one or more layers of copper and possibly one or more layersof another metal therein, e.g., an etching barrier metal such as nickel.The tips of the posts may have coplanar surfaces.

Thus, for example, substantially rigid posts may be patterned bylithography from a conductive sheet attached to dielectric element 50 toform solid metal posts extending upwardly above the top surface 52 ofthe dielectric element 50. Such processing tends to form metal postswhich have a frustoconical shape, wherein edges of the posts are slopedaway from the tips 42 of the conductive posts 40.

Similarly, the posts may be formed from a double etching process, suchas disclosed in commonly assigned U.S. Patent Application PublicationNo. 2008/0003402, filed on Mar. 13, 2007, the disclosure of which isincorporated herein by reference. Alternatively, the posts can be formedas disclosed in commonly assigned U.S. Patent Application PublicationNo. 2010/0044860 to Haba, filed on Jul. 30, 2009; or U.S. PatentApplication Publication No. 2009/0188706 to Endo, filed on Dec. 23,2008, of which all of the disclosures are incorporated herein byreference.

In addition, electrolytic plating methods for forming posts on a metalsubstrate are described in U.S. Pat. Nos. 6,372,620 and 6,617,236, eachto Oosawa et al., the disclosures of which are incorporated herein byreference. Unlike etching processes in which exposed portions of aconductive layer on a substrate are removed, substantially rigidconductive posts can be formed by depositing metal on the exposedportions of the substrate. Such posts may instead have a more uniformcircular shape, as opposed to a frustoconical shape that results fromthe etching process.

Referring to FIG. 1( c), a pre-determined amount of underfill can bedeposited onto the dielectric element 50 so that the underfill 60 coversthe exposed top surface 52 of the dielectric element 50 and posts 40. Inone exemplary embodiment, the underfill 60 can be spin coated over thetop surface 52 of the dielectric element 50 and top surfaces or tips 42of the posts 40. The edge surfaces 44 and tips 42 of the conductiveposts may contact the underfill 60 so that the posts are fully coveredby the underfill. (See FIGS. 1( c) and 2.) The underfill can include apolymeric component, which, after final package assembly and casingthereof, increases a rigidity of the mechanical connection between themicroelectronic and dielectric elements 30, 50.

Referring now to FIG. 1( d), the masses of bonding metal, e.g., solder10 on the microelectronic element 30 can be juxtaposed with theconductive posts 40 extending away from the dielectric element 50. Inthe embodiment shown, the masses of solder 10 can be moved toward theconductive posts 40, i.e., by moving the microelectronic element towardsthe substrate. Alternatively, the substrate with the conductive posts 40thereon can be moved toward the solder masses 10 of the microelectronicelement, or both the solder and conductive posts can be moved closer toone another. For example, the die 30 and the dielectric element 50 canbe placed on respective plates (not shown) and the conductive posts 40and solder 10 can be moved closer together by moving one or both of themicroelectronic element 30 or dielectric element 50 in one or both ofdirections 62,64. To ensure mating of the conductive posts 40 with thesolder 10, the solder 10 may be pressed into the underfill 60 so as toat least deform a portion of the underfill 60. In such arrangement, theunderfill 60 may contact the top surface 52 of the dielectric element 50and edge surfaces 44 of the solder 10, but may or may not contact thecontact-bearing surface 32 of the microelectronic element 30. In aparticular embodiment, the method may include a step to align theconductive posts with the masses of bonding metal. However, in somecases, it may be possible to join the posts of the dielectric elementwith the bonding metal on the microelectronic element without requiringa step of aligning the posts with the bonding metal. That is, thebonding metal may have a tendency to self-align the structures when thebonding metal is heated to a temperature at which it liquefies, at whichtime surface tension from the masses of bonding metal can help bring theconductive posts in better alignment with the masses of bonding metal.

Turning now to FIG. 1( e), the microelectronic element 30 can continuebeing moved toward the dielectric element 50 so that the tips 42 of theconductive posts 40 become embedded within the underfill 60. The tips 42will also at least deform at least a portion of the solder 10, if notfully penetrate the solder 10. In one embodiment, the conductive posts40 penetrate at least a distance D (FIG. 1( e)) which is at least 25% ofthe height H_(s) (FIG. 1( a)) of the solder 10 extending away from thecontact-bearing surface 32 of the microelectronic element 30. Forexample, if the height of the solder 10 is 100 microns above the surfaceof the microelectronic element 30, the conductive post can penetrateinto the solder 10 at least 25 microns.

As compared with prior art microelectronic packages, penetration of theunderfill 60 and deformation and/or penetration of the solder 10 by theconductive posts 40 can be made possible by the substantial rigidity andsharp edges (FIGS. 1 and 2) of the conductive posts 40. The structure ofthe conductive posts 40 enable them to puncture or push through theunderfill 60 and at least deform solder 10, if not become embedded inthe solder 10. Once the conductive posts have penetrated the underfilland at least deform a portion of the solder 10, the underfill 60 cancontact both the contact-bearing surface 32 of the microelectronicelement, as well as the top surface 52 of the dielectric element 50. Inalternative embodiments, in order to become embedded in the underfill 60and solder 10, the dielectric element 50 can be moved toward themicroelectronic element 30, or the microelectronic element 30 and thedielectric element 50 can be moved toward each other at the same time.

Referring now to FIG. 1( f), after the solder 10 and conductive posts 40have been joined together, the overall microelectronic package 100 maybe heated to a reflow temperature so that the solder 10 may flow aroundthe edges of the conductive post 40 to form a conductive column 90. Inan exemplary embodiment, the solder will wet the conductive post aheight Hc/2 that is at least 50% of the total height Hc of theconductive post. In a particular embodiment, the solder may cover thepost to the exposed surface 52 of the dielectric element or may coverany portion of the conductive post 40 between the height HC/2 and theportion of the top surface 52 of the dielectric element 50 adjacent thepost.

As shown, the height H_(p) of the conductive posts 40, the heightH_(solder) of the solder column 10A, and the bond pads 20 may contributetoward a separation distance X between the contact-bearing surface 32 ofthe microelectronic element and the top surface 52 of the dielectricelement 50. In an exemplary embodiment, the height H_(c) of theconductive posts 40 is at least forty percent (40%) of a separationdistance X between the top surface 52 of the dielectric element 50 andthe contact-bearing surface 32 of the microelectronic element 30. In oneexample, where the distance X can be 25 to 100 microns, the conductiveposts 40 have a height H_(c) of at least 10 microns. It is to beappreciated that the distance X may be taken between exposed topsurfaces of elements that may be provided on top of the contact bearingsurface 32 of the microelectronic element and the top surface of anelement provided on the top surface of a dielectric element, such as asolder mask, adhesive layer, or any other material that covers theexposed surfaces of the dielectric element or contact bearing surface 32of the microelectronic element.

Referring to FIG. 2A, an enlarged schematic view of a tip of one of theconductive posts in FIG. 1( f) is shown. As shown in exaggerated detail,at the joint between the solder 10 and conductive posts, residual traces62 of underfill 60 will be present in the solder 10. The residual traces62 of underfill 60 may be present or mixed in with the solder 10 whenthe conductive post 40 and/or the solder 10 are pressed toward oneanother. Referring back to FIG. 1(d), when the conductive post 40 andsolder 10 are juxtaposed with one another, a portion P of underfill 60is positioned between the solder 10 and tip 42 of the conductive post40. As the dielectric element 50 and microelectronic element 30 aremoved closer to one another (FIGS. 1( d) and 1(e)) and the conductivepost 40 becomes embedded within the solder 10, traces (not shown) of theunderfill 60 that were positioned between the solder 10 and conductivepost 40 will also become embedded within the solder 10. In effect, theconductive posts 40 may push the underfill 60 into the solder 10. Thesetrace portions 62 will appear at the juncture between the conductivepost 40 and solder 10.

It is to be appreciated that numerous modifications can be made to theembodiment of FIG. 1, some of which will be described in more detailherein. For example, the underfill 60 may be deposited over the topsurface 32 of the microelectronic element 30 (FIG. 4), as opposed to thedielectric element 50, or may be deposited on both the microelectronicelement 30 and dielectric element 50 (FIG. 8). A solder mask mayalternatively be deposited onto the dielectric element 50 (FIG. 3( a))or the conductive posts 40 may be coated, so as to limit the amount ofunderfill 60 and solder 10 that directly contacts the surface of eitherthe dielectric element 50 or microelectronic element 30 (FIG. 8). Thesolder mask or coating may also prevent the underfill 60 from contactingthe edges of the conductive posts extending from either the surface 32of the microelectronic element 30 or surface 52 of the dielectricelement 50. Instead of the solder or other bond metal 10 being placeddirectly on the bond pads 20, solder may alternatively be directlyplaced on one or more tips 42 of the conductive posts 40 (FIG. 6).

Referring now to FIG. 3, an alternative embodiment for a method ofmaking the microelectronic package 300 (FIG. 3( f)) is shown. Thisembodiment is similar to the one shown in FIG. 2 and follows the samesteps, starting with a microelectronic element 330 having a bond metal10 thereon (FIG. 3( a)) and a dielectric element 350 with posts 340thereon (FIG. 3( b)). The method of claim 3 only differs to the extentthat a solder mask 370 (FIG. 3( b)) is provided on the major surface 352of the dielectric element 350, which affects how much of the underfill360 and solder 310 can directly contact the conductive posts 340 and thesurface 352 of the dielectric element 350. In the example shown in FIG.3( b), the solder mask 370 may be provided across the top surface 352 ofthe dielectric element 350, such that the solder mask 370 contacts theside edges 344 of the conductive post 340. Alternatively, the soldermask may be spaced a distance from the edge 344′ of the conductive post340′, such that there is a gap G between the edge 374 of the solder mask370 and the edge 344′ of the conductive post 340′.

As shown in FIG. 3( c), the underfill 360 is permitted to flow over anexposed top surface 372 of the solder mask 370. As the solder mask 370is deposited over the dielectric element 350, the underfill 360 will notcontact the edge surfaces 344 of the lower portions or bases 346 of theconductive posts 340. The underfill 360 may therefore overlie andcontact the tips 342 of the conductive posts, and the edge surfaces 344of the conductive posts 340 that remain exposed and extend upwardly fromthe solder mask 370.

As shown in FIG. 3( e), after the dielectric element 350 andmicroelectronic element 330 are joined together (FIG. 3( d)), the solder310 deposited on the bond pads 320 of the microelectronic element 330may be deformed by the conductive posts or the conductive posts 340 maybecome embedded in the solder as the microelectronic element 330 ismoved towards the tips 342 of the conductive posts 340 on the dielectricelement 350. Once the tips 342 of the conductive posts 340 deform orbecome embedded in the solder 310, the package 300 can be reflowed. Inthe example shown, the solder mask 370 prevents solder 310 from wettingthe edges of the base 346 of the conductive post 340 which are in directcontact with the solder mask 370. Only the exposed portions of theconductive posts 340 extending above the surface 372 of the solder mask370 are wetted by solder 310.

Referring now to FIG. 3( f), after the solder 10 and conductive posts340 have been joined together, the overall microelectronic package 300may be heated to a reflow temperature so that the solder 310 may flowalong the edges of the conductive post 340 to form a conductive column390. As shown, because the solder mask 370 is deposited adjacent theedges 344 of the base 346 of the conductive post 340, the solder 310will only flow along and contact those edges of the conductive post 340extending away from and exposed above the surface 372 of the solder mask370. In contrast, where the solder mask 370 does not touch the edge ofthe conductive post 340′, the solder 310 may reflow to the base of theconductive post 340′ or adjacent the top surface of the dielectricelement 350.

Referring to FIG. 3( g) and similar to the previous embodiments, theheight H_(p) of the conductive posts 40 is measured from the top surface372 of the solder mask 370 to the top surface of the conductive post340. The height Hp may be at least forty percent (40%) of a separationdistance X between the top surface 332 of the microelectronic element330 and the exposed top surface 372 of the solder mask 370. In oneexample, where the distance X can be 25 to 100 microns, the conductiveposts 40 have a height of at least 10 microns.

Still referring to FIG. 3( g), once the microelectronic package 300 iscompleted, it may be electrically connected to a circuit panel 390 orcircuit board. Terminals 345 on the dielectric element 350 areelectrically connected with the posts 340 or other conductive elementsexposed at surface 352 thereof. As shown, solder balls 362 may be usedto connect the terminals 345 to contact pads 355 on the circuit panel.As an alternative to the use of solder balls 362, any other conventionalform of conductively connecting the microelectronic package 300 to thecircuit panel 390 may be used, such as conductive pins, other forms ofconductive material, or the like. It is to be appreciated that themicroelectronic package 300 can be electrically connected to any otherform of external element or device.

In FIGS. 4( a)-(f), another alternative embodiment of a microelectronicpackage 400 (FIG. 4( f)) in accordance with the present invention isshown. This embodiment is similar to the method described above withrespect to FIGS. 1-2, except that, as shown in FIG. 4( c), the underfill460 may alternatively be provided on the top surface 432 of themicroelectronic element 430, and may not be provided on the top surface452 of dielectric element 450. Referring to FIG. 4( d), once the solder410 on the microelectronic element 430 and the conductive posts 440 arejuxtaposed with one another and brought closer together, the tips 442 ofthe conductive posts 440 begin to penetrate through the underfill 460.In one embodiment, during this step, the underfill 460 will extend fromthe contact-bearing surface 432 of the microelectronic element 430 tocontact the conductive posts 440.

One or both of the microelectronic element 430 and dielectric element450 can then be moved toward the other so that the conductive posts 440can push through the underfill 60 and at least deform, if not alsobecome embedded within, the solder 410. In the embodiment shown, thetips 442 of the posts extend just into the solder 410, a distance D thatis at least 25% of the total height H_(s) of the solder 410 andconductive pad 420. Thereafter, the package 400 can be reflowed suchthat the solder 410 flows along the exposed edges of the conductive post440. As shown, because there is no solder mask or other coating on theconductive post 440 that would prevent wetting of the post by thesolder, the solder 410 flows along the conductive post 440 and may forma conductive column 490 of solder that extends from the bond pad 420 onthe microelectronic element to the base 446 of the conductive post 440extending upwardly from the dielectric element 450.

Referring now to FIG. 5, an alternative embodiment of FIGS. 1( a)-1(f)is shown. This embodiment is similar to the one shown in FIGS. 1(a)-1(f), but differs in that, in the initial component (FIG. 5( a)), theconductive posts 540 extend away from the contact-bearing surface 532 ofthe microelectronic element 530, as opposed to extending away from thesurface 552 of the dielectric element 550. Similarly, solder 510 mayextend from bond pads 520 exposed at the top surface 552 of thedielectric element 550 (FIG. 5( b)), and not the microelectronic element530 as in previous embodiments.

For ease of reference, directions are stated in this disclosure withreference to a “top”, i.e., contact-bearing surface 532 of asemiconductor chip. Generally, directions referred to as “upward,”“rising from” or “extending from” shall refer to the directionorthogonal and away from the microelectronic element top surface 532.Directions referred to as “downward” shall refer to the directionsorthogonal to the element top surface 532 and opposite the upwarddirection. A “vertical” direction shall refer to a direction orthogonalto the chip top surface. The term “above” a reference point shall referto a point upward of the reference point, and the term “below” areference point shall refer to a point downward of the reference point.It is to be further appreciated that similar reference numerals will beused to describe similar elements.

The method steps are otherwise similar to those previously discussedherein. Referring to FIG. 5( c), an underfill 560 may be provided overthe bonding metal, e.g., solder 510 extending from the dielectricelement 550. In this embodiment, the underfill 560 also covers thesurfaces 514 of the solder 510 in its entirety. Turning to FIG. 5( d),the conductive posts 540 can be juxtaposed with the solder 510, suchthat the conductive posts 540 are able to become embedded within orpenetrate through the underfill 560. As shown in FIG. 5( e) anddiscussed in previous embodiments, the tips 542 of the conductive posts540 extend through the solder 510. Once reflowed, the underfill 560 cancontact the exposed edges 544 of the conductive post 540. Similar to theembodiment described above with reference to FIG. 1( f), the solder maycontact a portion of or all of the height Hc of the post above thesurface 532 of the microelectronic element. In an exemplary embodiment,the solder may contact at least half of the height of the post from thesurface 532. As particularly shown in FIG. 5( f), when there is nosolder mask and/or other material coated on the conductive posts thatwould prevent the solder 510 from wetting any portions of the conductivepost 540, a conductive column 590 of solder can, in one embodiment,extend from the contact-bearing surface 532 of the microelectronicelement 530 to the contacts 520 exposed at the surface 552 of thedielectric element 550.

Referring now to FIG. 6, another method of making a microelectronicpackage 600 (FIG. 6( e)) in accordance with the present invention isshown. The method is similar to those previously disclosed herein, butdiffers to the extent that conductive posts 640A extend from themicroelectronic element 630 (FIG. 6( a)) and conductive posts 640B alsoextend from the dielectric element 650 (FIG. 6( b)). Furthermore, solder610 may be deposited directly on the tips 642 of the conductive post640A and solder mask 680 may be provided adjacent the conductive posts640A. For example, an exposed layer of silicon nitride can serve as amask 680 to avoid wetting of the surface 632 of the microelectronicelement 630 by a bond metal such as solder.

As shown in FIG. 6( c), an underfill 660 is deposited over theconductive posts 640 extending from the top surface 652 of thedielectric element 650. The conductive posts 640A and conductive posts640B may then be juxtaposed with one another (FIG. 6( d)). The tips 642of the conductive posts 640A, as well as the solder 610 on the tips 642thereof, may be pressed into the underfill 660, such that the tips 642and solder 610 thereon may extend into at least a portion of theunderfill 660. The dielectric element 650 and microelectronic element630 may continue to be pressed together (or one toward the other) untilthe tips 642B are able to penetrate into at least a portion of thesolder 610, such that at least 25% of the original height H_(s) of thesolder 610 (FIG. 1( e)) is penetrated by the conductive post 640B. (FIG.6( e).) Thereafter, the package may be reflowed to cause the solder 610deposited on the tip 642A of the conductive post 640A to flow and wetthe edges of both conductive posts 640A, 640B (FIG. 6( f)). In thisembodiment, as shown in FIG. 6( f), because a limited amount of solder610 is deposited on the tips 642A of the conductive posts 640A, thesolder 610 may not fully wet the respective edges 644A, 644B of therespective conductive posts 640A, 640B. As shown, the base 646 of theconductive posts 640B may remain exposed and capable of being in directcontact with the underfill 660.

Referring now to FIG. 7, an alternative method of FIG. 6 is shown. Inthis embodiment, dielectric element 750 also supports posts 740B.However, in contrast to the embodiment of FIG. 6, there is no soldermask that extends along the length of microelectronic element 630 (FIG.7( a)). The underfill 760 is deposited over the exposed portions of thecontact-bearing surface 732 of the microelectronic element 730, as wellas the exposed portions of the conductive post 740A that are not coveredby the solder 710. In the embodiment shown, the underfill preferablyextends beyond the outer edges of each of the conductive posts 740A.(FIG. 7( c).) It is to be appreciated that in alternative embodiments,the solder may instead be placed on the conductive post extending fromthe dielectric element 750.

Turning now to FIG. 7( d), the conductive posts 740A and solder 710extending therefrom, as well as the conductive posts 740B extending fromthe dielectric element 750 are juxtaposed with one another. Thedielectric element 750 and microelectronic element 730 can be pressedtogether so that the conductive posts 740B enter the underfill 760.

As further seen in FIG. 7( e), once the conductive posts 740B penetratethrough the underfill 760, the dielectric element 750 andmicroelectronic element 730 can continue being compressed until theconductive posts 740B are embedded within the solder exposed at theconductive tips 742A of the conductive post 740A extending from themicroelectronic element 730. The package can then be reflowed so thatthe solder 710 will wet the edges of the exposed surfaces of theconductive posts 740A and 740B (FIG. 7( f)).

Referring now to FIG. 8, another microelectronic package 800 (FIG. 8(e)) in accordance with the present invention is shown. As shown, themicroelectronic package includes two dielectric elements 850A (FIG. 8(a)) and 850B (FIG. 8( b)) that are substantially the same length.Referring to FIGS. 8( c 1) and 8(c 2), an underfill layer can bedeposited over the top surfaces 852A, 852B of the respective dielectricelements 850A and 850B. The dielectric element 850B may includeconductive posts 840 extending away from the top surface 852B of thedielectric element 850. The bases 846 of the conductive posts 840 may becoated with a material, such as a solder mask material or any organic orinorganic material that can help to prevent wetting of the conductiveposts by solder or other material.

As shown in FIG. 8( d), the conductive posts 840 can be juxtaposed withsolder 810 extending from the dielectric element 850A. Referring to FIG.8( e), the dielectric elements 850A and 850B can continue to be movedcloser together to place the conductive post 840 in contact with thesolder 810. In this embodiment, the solder 810 is not pierced orpenetrated by the conductive post 840. As shown, the conductive posts840 only deform the solder 810 extending from the dielectric element850A. Turning to FIG. 8( f), once the package is reflowed, the solder810 will flow along the edges of the conductive post 840 except wherecoated by the material 848 to prevent wetting of the bases 846 of theconductive posts 840.

Referring to FIG. 9, another alternative microelectronic package 900 isshown. This embodiment is similar to the prior methods of creating amicroelectronic package, and only differs to the extent that theconductive elements (i.e., conductive posts 940, solder 910, andconductive posts 920) are supported by respective microelectronicelements 930A, 930B, and none extend from a dielectric element. Theunderfill 960 encapsulates the interior of the package between the twomicroelectronic elements 930A, 930B.

Referring to FIG. 10, another alternative portion of a microelectronicassembly is shown. FIG. 10, which is an alternative view of a portion ofFIG. 1( f), shows that a conductive pad 1023 may be positioned on orwithin a first dielectric element 1050. A dielectric layer 1051 can beformed over dielectric element 1050 and an opening 1056 can be formedtherein. The conductive post 1042 can be formed by plating up throughthe opening and forming a post, or alternatively, depositing acontinuous metal layer over the dielectric layer 1051 and within theopening 1056 and then etching the continuous metal layer to form thedesired post size and shape.

The various microelectronic assemblies discussed above can be utilizedin construction of diverse electronic systems. For example, as shown inFIG. 11, a system 1900 in accordance with a further embodiment of theinvention includes a structure 1906 as described in the priorembodiments of microelectronic assemblies above in conjunction withother electronic components 1908 and 1910. In the example depicted,component 1908 is a semiconductor chip whereas component 1910 is adisplay screen, but any other components can be used. Of course,although only two additional components are depicted in FIG. 11 forclarity of illustration, the system may include any number of suchcomponents. The structure 906 as described above may be, for example, acomposite chip or a structure incorporating plural chips. In a furthervariant, both may be provided, and any number of such structures may beused. Structure 1906 and components 1908 and 1910 are mounted in acommon housing 1901, schematically depicted in broken lines, and areelectrically interconnected with one another as necessary to form thedesired circuit. In the exemplary system shown, the system includes acircuit panel 1902 such as a flexible printed circuit board, and thecircuit panel includes numerous conductors 1904, of which only one isdepicted in FIG. 11, interconnecting the components with one another.However, this is merely exemplary; any suitable structure for makingelectrical connections can be used. The housing 1901 is depicted as aportable housing of the type usable, for example, in a cellulartelephone or personal digital assistant, and screen 1910 is exposed atthe surface of the housing. Where structure 1906 includes alight-sensitive element such as an imaging chip, a lens 1911 or otheroptical device also may be provided for routing light to the structure.Again, the simplified system shown in FIG. 11 is merely exemplary; othersystems, including systems commonly regarded as fixed structures, suchas desktop computers, routers and the like can be made using thestructures discussed above.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

The invention claimed is:
 1. A method for making a microelectronicassembly, comprising: providing a microelectronic element having a firstsurface and first conductive elements projecting above the firstsurface, and a dielectric element having a second surface and secondconductive elements projecting above the second surface, at least someof the first conductive elements or at least some of the secondconductive elements being substantially rigid conductive posts, and theother of the first or second conductive elements including a bond metaljuxtaposed with the at least some conductive posts, the posts having aheight above the respective surface from which the posts project, and anunderfill layer overlying at least some of the first conductive elementsor at least some of the second conductive elements, the posts includingtips having coplanar surfaces; moving at least one of the firstconductive elements towards the other of the second conductive elementssuch that the tips of the substantially rigid posts pierce the underfilllayer and at least deform the bond metal; and heating themicroelectronic element and the dielectric element to a joiningtemperature until the bond metal flows along edges of the posts tocontact the edges along at least one half the height of the posts andelectrically joins the microelectronic element with the dielectricelement, wherein the height of the posts above the surface from whichthey project is at least forty percent of a distance between the firstand second surfaces, and wherein prior to the step of deforming the bondmetal, trace amounts of the underfill layer are pushed into the bondmetal by the conductive posts.
 2. The method according to claim 1,wherein the first conductive elements include the bond metal and the atleast some conductive posts are second conductive elements of thedielectric element.
 3. The method according to claim 1, wherein the atleast some posts are first conductive elements of the microelectronicelement and the second conductive elements include the bond metal. 4.The method of claim 1, wherein the step of moving at least one of thefirst conductive elements towards the other of the second conductiveelements includes the substantially rigid posts piercing the bond metal.5. The method of claim 1, wherein the step of moving at least one of thefirst conductive elements toward the other of the second conductiveelements includes penetrating the bond metal to a depth of at least 25%of a height of the bond metal above the respective one of the first orsecond surfaces.
 6. The method of claim 1, wherein at least some of thefirst conductive elements are substantially rigid posts.
 7. The methodof claim 1, wherein at least some of the first conductive elements areconductive pads.
 8. The method of claim 1, wherein the underfilloverlies the first conductive elements.
 9. The method of claim 1,wherein the underfill overlies the second conductive elements.
 10. Themethod of claim 1, wherein the underfill overlies the first and secondconductive elements.
 11. The method of claim 1, wherein at least some ofthe first conductive elements are substantially rigid posts, and atleast some of the second conductive elements are substantially rigidposts.
 12. The method of claim 1, wherein the posts are etched posts.13. The method of claim 1, wherein the step of moving occurs after thestep of providing.
 14. The method of claim 1, wherein at least some ofthe second conductive elements are substantially rigid posts.
 15. Themethod of claim 14, wherein the step of providing includes providing abond metal on the at least some of the substantially rigid posts. 16.The method of claim 1, wherein at least some of the second conductiveelements are contact pads.
 17. The method of claim 16, wherein the stepof providing includes providing a bond metal on the at least some of thecontact pads.
 18. The method of claim 1, wherein both the firstconductive elements and the second conductive elements are substantiallyrigid posts.
 19. The method of claim 18, wherein tips of the firstconductive elements and tips of the second conductive element arecoplanar.